Pulse capture unit and apparatus for controlling the blending of two flowable substances

ABSTRACT

A device is described which will accept trains of pulse signals on inputs thereof and will provide corresponding trains of pulse signals on corresponding outputs such that the number of pulse signals in the train at any of these outputs is equal to the number of pulse signals on the train at the corresponding input and such that there is never coincidence of pulse signals on these outputs regardless of whether or not there is coincidence of pulse signals on the inputs. In application of the device to a blending system two pipe lines for fluids to be blended have respective pulse transducers connected to respective inputs of such a device. The transducer for the minor component of the blend provides its pulses via said device to a counter which on reaching a predetermined count corresponding to the volume of the minor component in a standard quantity of the desired blend produces a signal to close a valve in the minor component flow line. The pulses at both outputs of said device are counted together by a further counter which on reaching a count corresponding to said standard quantity re-sets the first mentioned counter causing said valve in the minor component flow line to open again.

United States Patent [191 Storey Dec. 11, 1973 PULSE CAPTURE UNIT ANDAPPARATUS FOR CONTROLLING THE BLENDING OF TWO FLOWABLE SUBSTANCESWilliam Arthur Storey, Little Beeches, Ashley Park Ave,Walton-on-Thames, England [22] Filed: Jan. 10, 1972 [21] Appl. No.:216,492

[76] Inventor:

[30] Foreign Application Priority Data Primary Examiner-Robert B. ReevesAssistant Examiner-David A. Scherbel Attorney-Paul Bogdon [57] ABSTRACTA device is described which will accept trains of pulse signals oninputs thereof and will provide corresponding trains of pulse signals oncorresponding outputs such that the number of pulse signals in the trainat any of these outputs is equal to the number of pulse signals on thetrain at the corresponding input and such that there is nevercoincidence of pulse signals on these outputs regardless of whether ornot there is coincidence of pulse signals on the inputs. ln applicationof the device to a blending system two pipe lines for fluids to beblended have respective pulse transducers connected to respective inputsof such a device. The transducer for the minor component of the blendprovides its pulses via said device to a counter which on reaching apredetermined count corresponding to the volume of the minor componentin a standard quantity of the desired blend produces a signal to close avalve in the minor component flow line. The pulses at both outputs ofsaid device are counted together by a further counter which on reachinga count corresponding to said standard quantity resets the firstmentioned counter causing said valve in the minor component flow line toopen again.

15 Claims, 2 l )rawi n g Figures PULSE CAPTURE UNIT AND APPARATUS FORCONTROLLING THE BLENDING OF TWO FLOWABLE SUBSTANCES This inventionrelates to a device for producing at each of a plurality of outputsthereof a train of pulses each corresponding to a respective pulse at arespective input of the device, such that pulses on respective saidoutputs are never coincident regardless of whether or not pulses at therespective inputs are coincident, and the invention also relates toblending control means for flowable materials utilising such a device.

According to one aspect of the invention such a device includes meansarranged to produce pulses at a plurality of outputs thereof in arepeating sequence (also called a pulse sequence means), and a pluralityof units each having an input and an output, and each arranged to detectthe occurrence of a signal at its input during a complete sequence andto deliver a pulse at its said output on the occurrence of a pulse onthe respective output of said first mentioned means.

Further aspects of the invention will be apparent from the followingdescription with reference to the accompanying drawings in which:

FIG. 1 is a schematic diagram of a device according to the invention,and

FIG. 2 is a schematic diagram of a fuel blending and costing apparatususing the device of FIG. 1.

Referring to FIG. 1, the device shown therein has inputs 10a and 10b andoutputs 12a and 12b and it is the purpose of the device to produce atthe output 12a a pulse for every pulse received at the input 10a, and atthe output 12b, a pulse for every pulse received at the input 10b, suchthat a pulse on the output 12a can never coincide with a pulse at theoutput 12b regardless of whether or not there is coincidence of thecorresponding pulses at the inputs 10a and 10b.

The device includes an oscillator 14 the output of which is fed to acounter 16 having an associated decoder 18 with four output lines 20,22, 24 and 26 the decoder being arranged so that for successiveoscillator pulses produced, a pulse of the same length as thecorresponding oscillator pulse will appear only on the line 20, at thenext oscillator pulse a similar pulse will appear only on the line 22,at the next oscillator pulse a similar pulse will appear only on theline 24, at the next oscillator pulse a similar pulse will appear onlyon the line 26, at the next only on the line 20 and so on.

The frequency of the oscillator is chosen so that its period is lessthan one-fourth of the minimum pulse length, and less than one-fourth ofthe minimum spacing between pulses, of the pulse trains to be applied ateither of the inputs 10a or 10b.

The input 10a is connected to a unit comprising a NAND gate 30a with twoinputs one of which is connected to the input 10a. The output of thegate 30a is connected to the set input of a crossed NAND gate flip-flopcomprising NAND gates 31a and 32a. The output of the latter flip-flop isconnected to one input of a three input NAND gate 34a the output ofwhich is connected via an inverter 36a to the output 12a. The output ofthe invertor 36a is connected to a re-set input of a flip-flop 38ahaving its output connected to another of the inputs of the NAND gate340.

The input 100 is also connected via an inverter 40a to one input of aNAND' gate 42a the output of which is connected to a set input of theflip-flop 38a and to the re-set input of the flip-flop 31a, 32a. Theother input of the NAND gate 42a is connected to output line 24 theother input of the NAND' gate 30a is connected to the line 20 and theremaining input of the NAND gate 34a is connected to the line 22.

Considering the device in the state in which the flipflop 31a, 32a isproviding a zero signal i.e. an inhibiting signal at the respectiveinput of the gate 34a and the flip-flop 38a is providing a 1 signal atthe respective input of the gate 340, if there is no pulse signalpresent on the line 10a, then a 1 signal will be present on the outputof the gate 300, whatever the condition of line 20. Thus a pulseappearing on the line 20 will have no effect. A succeeding pulse on theline 22 will have no effect since the gate 34a is inhibited by theflip-flop 31a, 32a and as a result a 1' signal will remain at the outputof the gate 34a and a zero signal will remain at the output 12a. On theoccurrence of a succeeding pulse on the line 24 the output of the gate42a will change from a l to a zero providing a re-setting signal to theflipflop 31a, 32a and a setting signal to the flip-flop 38a but sincethose are already in their re-set and set conditions respectively therewill be no change, so that as long as there is no pulse signal at theinput 10a.

Suppose now that a pulse signal appears on the input 10a, let us sayimmediately after the termination of a pulse on the line 20. Thesequence will be exactly as before (except that the output of the gate420 will not change to zero on the appearance of a pulse on the line 26)and the state of the device so far described will be unchanged until thenext pulse on line 20 appears. The pulse on the line 10a will still bepresent since the minimum pulse length is greater than four times theoscillator period. At the occurrence of the pulse on the line 20, theoutput of the gate 30a will change to zero, setting the flip-flop 31a,32a, so that the inhibiting signal applied thereby to the gate 34a isremoved so that on the occurrence of the next pulse on the line 22, thelatter pulse will be gated through the gate 34a and invertor 36a toprovide at the output 12a a 1 pulse signal of the same duration as thecorresponding oscillator pulse.

The latter signal will also re-set the flip-flop 38a so that the latterwill now provide an inhibiting signal to the gate 340.

While the pulse signal remains on the input the flip-flop 31a, 32a and38a can never be re-set and set by the gate 42a during continued runningof the oscillator so that no more than one pulse at the output 12a canbe produced as a result of a single pulse at the input 10a.

The input 10b and output 12b are connected to a circuit unit identicalwith that to which the input 10a is connected, the corresponding partsbeing similarly numbered but having the suffix b instead of the suffixa. However the gate 30b has one of its inputs connected to the line 22,the gate 34b has its remaining input connected to the line 24 and thegate 42b has its other input connected to the line 26.

Thus each signal on the output 12a is coincident with a pulse on theline 22 while each signal on the output 12b is coincident with a pulseon the line 24. The flipflops 38a and 38b have further re-set inputsconnected to an initial re-set line 50.

Referring to FIG. 2 there is shown an apparatus for producing variousblends of two grades of fuel, A and B and for measuring and indicatingthe total volume and calculating and indicating the corresponding costto the customer.

The apparatus includes two pumps 60a and 60 b for the respective fuelgrades, the pumps feeding respective fuel lines in which are disposedrespective stop valves 62a and 62b which are either fully open or fullyclosed, respective flow reduction valves 64a and 64b which are eitherfully open or partially closed, and respective transducers 66a and 66beach arranged to provide a series of pulses to a respective input a or10b of the device of FIG. 1, which is indicated at 68. Downstream of thevalves and transducers the fuel lines unite and are connected to asingle dispensing nozzle (not shown). Each pulse from each transducercorresponds to a predetermined unit of volume of the respective fuelpassed through the respective flow line.

The outputs 12a and 12b of the device 68, (which is hereafter called apulse capture unit) are connected to respective inputs of an OR gate 70,the output of which is connected to a counter 72 driving a display 74indicating the total volume of fuel dispensed in a dispensing operation.The counter 72 also drives a fraction decoder 76, (the function of whichwill be described later), the decoder in turn controlling a start signalgenerator 78.

The outputs 12a and 12b are also connected to respective costing units80a and 80b, which may be constructed as described in my co-pendingapplication Ser. No. 216,670, filed Jan. 10, 1972, 10249/70, or No.41764/71 or No.4l765/7l.

Each of these costing units provides for a train of input pulses eachrepresenting a unit of volume of the fuel grade concerned, a train ofoutput pulses each representing a unit of currency in the correspondingcost of the fuel concerned.

Since the pulses on the outputs 12a and 12b are non coincident they canbe added together via the OR gate 70 in the counter 72 without error,similarly since the output of each costing unit 80a is synchronised withthe input pulses applied thereto and since the latter are nevercoincident for the two costing units, the output pulses of the costingunits are non coincident. These output pulses are passed to respectiveinputs of an OR gate 82, the output of which is connected to the inputof a counter and display 84, so that the latter will indicate the totalcost of the fuel dispensed in a dispensing operation.

The outputs 12a and 12b are also connected to respective contacts of atwo way switch 86 having an output line 87 connected to a counter 88. Inone position of the switch 86 the output 12a is connected to the inputof the counter 38 while in the other position of the switch 86 theoutput 12b is connected to the input of the counter 88. The counter 88is also connected to a binary number comparator 90 which is alsoconnected to a blend select unit 92. The blend select unit is arrangedin response to a manual selection of the desired blend made thereon topresent to the comparator 90 a corresponding number. The number systemutilised by the counter 88, the comparator 90 and the blend select unit92 may be binary or binary coded decimal.

The comparator 90 is arranged to provide on an output line 94 thereof asignal when the count in the counter 88 becomes equal to the numberpresented by the unit 92 and is arranged when the count in counter 88reaches a value equal to a predetermined fraction, eg to percent, of thenumber presented by the unit 92, to provide a signal on a line 96thereof.

The line 96 is connected to a signal generator 98 having an outputconnected to an input of the two way switch 100, which in one positionconnects the output of the generator 98 with the valve 62a and in itsother position connects the output of the generator 98 with the valve62b. The valves 62a and 62b are of course electrically operated as arethe valves 64a and 64b.

The control inputs of the valves 64a and 64b are connected to the inputsof respective two way switches 102a and 102b, each of which in oneposition thereof connects the respective valve 64a, 64b directly with aline connected to the output of a signal generator 104, having its inputconnected to the output 94. In the other positions of the switches 102a,l02b the respective valves 64a and 64b-are connected to the output of aninvertor 106 having its input connected to the output of the generator104.

The arrangement is such that when a signal appears on the line 94, ifthe valve 64a or 64b is connected to the input of the invertor 106 thenthe respective valve 64a or 64b will be moved from its positionpermitting full flow through the respective fuel line to its positionpermitting only reduced flow through said line, whereas if the valve 64aor 64b is connected directly to the output of the generator 104, therespective valve 64a or 64b will be moved from its position permittingonly reduced flow to its position permitting full flow.

In either case the valves 64a or 64b will change back to their initialpositions on removal of the signal at the output 94. Similarly on theappearance of a signal at the output 96, the valve 62a or 62b connectedby the switch 100 to the output of the generator 98 is moved from itsopen to its closed position and on the removal of said signal returns toits open position. Whichever valve 62a, 62b has its control inputisolated by the switch 100 is open.

The blend select unit 92 is arranged when a blend selection is madethereon, to move the switch 86 to the position in which the counter 88is connected to the output 12a or 12b which is associated with thetransducer 66a or 66b in whichever of the fuel lines is the line for thefuel grade which forms the minor component of the blend selected, (whichgrade is hereinafter referred to as the minor grade). At the same timethe unit 92 moves the switch 100 to the position in which the signalgenerator 98 is connected to the stop valve for the minor grade, andmoves the switches 102a and 102b to the positions in which the switch102a or l02b connected with the minor grade valve 64a or 64b isconnected to the output of the invertor 106, and in which the otherswitch 102a or l02b is connected directly to the output of the signalgenerator 104.

The switches 86, 100, 102a and 102b are ganged in practice as shown bythe dotted line, so that they are all switched over in unison by theunit 92. The switches may be either mechanical or electronic in nature.

In the position shown in FIG. 2 the grade A has been selected as theminor grade.

Let us suppose that each of the transducers 66a and 66b is arranged toprovide 200 pulses per gallon of the respective fuel grade dispensed andthat it is desired that the blend should be accurate if a whole numberof tenths of a gallon of blended fuel is dispensed. In this case forevery 20 pulses added to the count in the counter 72 a signal will bepassed to the start signal generator 78, the output of which isconnected to a reset input of the counter 88.

On receipt of a signal from the decoder 76 the signal generator 78passes a signal to the counter 88 to re-set the latter to zero. In theexample chosen let us suppose that it is desired to dispense a blend of3 parts grade B, to 1 part grade A. The unit is set accordingly and theswitches 86, 100 and 102 are set in the positions shown for grade A asthe minor grade.

The unit 92 presents signals representing the number 5 to the comparator90. The unit 68, the counter 72 and the costing units 8a and 80b are setto zero at the beginning of the dispensing operation by signals appliedto reset inputs thereof while the counter 88, for reasons connected withthe nature of the logic circuitry used, is set to its maximum count, anumber higher than that presented by the unit 92. These re-set signalsmay, for instance, be generated by the closing of a switch on lifting ofa dispensing nozzle before fuel dispensing be gins. Thus at this stagethere are signals both on the lines 94 and 96 so that the valves 62b and64b are fully open and the valve 62a is closed and the valve 64a is inits position to restrict therethrough. Assuming that dispensing hasbegun and both pumps 60a, 60b are running a first pulse will be producedby the transducer 66b after one two-hundredth of a gallon of grade B hasbeen dispensed.

Now the decoder 76 is arranged to cause the signal generator to providea pulse on the arrival at the counter 72 of the first pulse after theinitial re-set, so that the counter 88 is set to zero and the signals onthe outputs 94 and 96 are removed by the comparator 90 so that the valve64b is moved to ist reduced flow position, the valve 62a is opened andthe valve 64a moved to its full flow position. Both the transducers 66aand 66b are not producing pulses and corresponding pulse trains appearon the outputs 12a and 12b of the pulse capture unit, and are combinedin the gate 70 and counted in the counter 72. The two pulse trains leadto corresponding price pulse trains being produced by the costing units80a and 80b and the total cost is counted up in the counter 84 andclocked up continually on the display thereof.

The pulses from the output 12a are passed to the counter 88 and arecounted thereby. After four pulses (in the example under consideration)have been counted by the counter 88 a signal is applied to the output 94by the comparator 90 so that the pulse generator 104 provides a signalcausing the valve 64a to move to its reduced flow position and causingthe valve 64b to move to its full flow position, and the next pulseappearing at the output 12a from the minor flow transducer beings thecount in the counter 88 to 5 so that the comparator 90 provides a signalalso on its output 96 causing the generator 98 to close the valve 62a sothat flow of minor grade is cut off entirely. When the count in counter72 reaches the decoder 76 causes the signal generator 78 to set thecounter 88 to zero once more so that the cycle repeats until dispensingceases. It will. be seen that in effect what is done is that a quantityof minor flow grade accurately measured is first mixed with a smallerquantity of major flow grade and the volume then brought up to 0.1 of agallon by adding further major flow grade, for each whole 0.1 of agallon dispensed. Thus the blend will be accurate if a whole number oftenths of a gallon have been dispensed except that there may be up toone twohundredth of a gallon more of grade B in the total volumedispensed than there ought to be for strict accuracy (due to the initialsetting of grade A no flow, grade B restricted flow). If a whole numberof tenths of a gallon have not been dispensed then there may be slightlymore of grade A (less than one-fourtieth of a gallon) in the totalquantity dispensed than there ought to be in the total quantitydispensed. Asssuming that more than one gallon is dispensed, which willnormally be the case in petrol vending applications the accuracy of theblend will be more than adequate. Indeed if the unit 92 and the decoderare arranged so that strict accuracy of blend is obtained only if awhole number of A gallons is dispensed, this may well be sufficient fornormal applications. It will be appreciated that the smaller the volumeis made over which the blend is accurate the nearer one approaches thesituation where the blend is accurate for any volume dispensed.

The principal limitation on the closeness with which the lattersituation may be approximated is the operating speed of the valves 64a,64b and 62a, 62b. The operation sequence of the valves, in which theflow reduction valve is operated to reduce the minor grade flow beforethe minor grade stop valve is operated reduces the error in blendingwhich would be caused by the operating time of the stop valve if onlythe latter were present.

In the petrol dispensing application assuming a full flow rate for eachfuel line of 12 gallons per minute, and assuming that blend ratios of3:1, 1:1 and 1:3 of grade A to grade B need only be provided, i.e. fivegrades of fuel in all, counting straight grade A and straight grade B,then if the unit 92 and the decoder 76 are set so that the blend will beaccurate over multiples of one-fifth of a gallon; then the minimumperiod between successive operations of any one of the valves 62a, 62b,64a or 64b will be more than one second, which is a long time comparedwith the operating time of the valves of the sleeve type which may beused.

It should be noted that whatever inaccuracies there may be in the blenddispensed, the cost indicated by the display of the counter 84 will becorrect since the costs of the actual quantities dispensed from the twofuel lines are calculated separately then added together.

It will be appreciated that the apparatus of FIG. 2 is of use in otherapplications than that of petrol vending. Indeed the apparatus could beused for blending any two flowable substances, for example liquids,powders or even gases, with any consequent necessary modifications tothe valves 62a, 62b, 64a, and 64b and the pumps 60a and 60b or theirreplacement by equivalent constructions. V

In some of these other applications it may be desired to provide forcontinuous adjustment of the blend over a range, and in this case theunit 92 may be provided with a manually rotatable knob rotation of whichcontinuously changes some variable the change of which is detected bymeans including an analog to digital convertor providing a digitaloutput to the comparator corresponding to the setting of the knob. As anexample the knob may control a variable potentiometer.

In the petrol vending application such refinement is unnecessary and itwill be sufficient for the manual setting means of the unit 92 toincorporate a multiposition switch, each position corresponding to adifferent blend. In its positions corresponding to straight grade A andstraight grade B, the unit 92 might be arranged to operate the switches86, 100 and 102 to select as the minor grade the grade which will not bepresent in the dispensed fluid and to hold the counter 88 permanently atits maximum count so that the minor grade valve 62a, 62b is permanentlyclosed and both valves in the major flow line are permanently open.

There are various simpler blending and costing devices which may beutilized incorporating the pulse capture unit, in which the pumps forgrade A and grade B to be blended are set mechanically to provide adesired blend. In one such device each fuel line has a transducerassociated therewith and supplies pulses to respective inputs of a pulsecapture device and the outputs of the latter are connected to respectiveinputs of an OR gate the single output of which is connected to aquantity counter and display and to a single costing unit which is setto calculate and display the cost of the fuel dispensed on the basis ofthe price per unit volume of the blend selected, said price beingselectable in accordance with the blend selected mechanically via thepumps for the two grades.

In this arrangement of course the total price displayed will be correctonly if the blend itself is correct, and thus the accuracy of the pricedisplayed depends on the accuracy of the mechanical blending controlsystem.

Another such device differs from that last described only in thatinstead of a single costing unit being connected to the output of the ORgate receiving the signals from the pulse capture unit, two separatecosting units are provided each connected to a respective output of thepulse capture unit, and each being set to calculate the price of therespective quantity of the respective grade dispensed. As with theapparatus of FIG. 2 the outputs of these costing units are addedtogether and the result shown on a final display which will thus displayaccurately regardless of any inaccuracy in the mechanically controlledblending system.

While the apparatus described has been referred to as operatingelectronically it will be appreciated that equivalent logic systemsoperating e.g. pneumatically or hydraulically may be used.

With regard to the apparatus of FIG. 2 it will be appreciated that wherethe apparatus is to be used for blending other than with a view to sale,the costing units 80a and 80b may be omitted.

I claim:

1. Apparatus for controlling the blending of two flowable substances,comprising separate dispensing means for each of said substances, acontrol means for at least one of said dispensing means operableselectively to cause said one dispensing means to dispense itsrespective substance and to arrest dispensing of its respectivesubstance, a transducer associated with each of said dispensing meansand arranged to produce a pulse each time a predetermined quantity ofthe respective substance is dispensed, a pulse capture unit having twoinputs each connected to a respective one of said transducers forreceiving pulses produced thereby and corresponding outputs at whichpulses are produced corresponding to the pulses applied to thecorresponding input, said pulses appearing at the respective outputs ofsaid pulse capture unit being noncoincident first counting means forcounting the pulses appearing on one of the corresponding outputs ofsaid pulse capture unit and corresponding to the pulses produced by thetransducer associated with said one dispensing means, second countingmeans for counting together the pulses appearing on both of saidcorresponding outputs of the pulse capture unit, said second countingmeans having associated therewith means arranged to operate the controlmeans for said one dispensing means each-time that a secondpredetermined number of pulses has been counted by said second countingmeans since the preceding operation of said control means and said firstcounting means having associated therewith means arranged to operatesaid control means for said one dispensing means to cause tha latter tocease dispensing when a first predetermined number of pulses smallerthan said second predetermined number has been counted thereby since thepreceding operation of said control means by said means associated withsaid second counting means, the relative mean flow rates of saiddispensing means during each period in which both dispensers aredispensing being such that the ratio of the mean flow through said onedispensing means to the mean total flow in said period is greater thanthe ratio of quantity of substance dispensed by said one dispensingmeans to the total quantity in the desired blend, and said first andsecond predetermined numbers being in the last mentioned ratio.

2. The apparatus of claim 1 wherein said pulse capture unit includesrespective pulse output means associated with each said input and arespective one of said outputs, pulse sequence means for operating saidpulse output means repeatedly at different times, each said pulse outputmeans including means for detecting the occurrence ofa pulse signal onits associated input and for storing said signal until operated by saidpulse sequence means, each said pulse output means including means fordelivering a signal to the associated output, if and only if a signalhas occurred at its associated input since the preceding operationthereof by said pulse sequence means said pulse sequence means beingarranged so that no two of said pulse output means are operable therebyat the same time, whereby the device will produce at each of saidoutputs thereof a train of pulses each corresponding to a respectivepulse at the associated input of the device and pulses on respectivesaid outputs are noncoincident 3. The apparatus of claim 2 wherein saidpulse sequence means has a plurality of control outputs and is arrangedto produce pulse signals at said control outputs in a repeatingsequence, and each said pulse output means is arranged to be operated todeliver a pulse at the associated output of the device if a signal isstored in said means associated with said output, on the occurrence of apulse on an associated one of said further outputs of said pulsesequence means.

4. The apparatus of claim 3 wherein said pulse sequence means comprisesan oscillator, a counter for counting the periods of said oscillator anda decoder driven by said counter decoder having a plurality of outputsconstituting said control outputs of the pulse sequence means, thedecoder being arranged to apply pulse signals in a repeating sequence tosaid control outputs thereof as successive oscillator periods arecounted by said counter.

5. The apparatus of claim 3 for use where the pulse length and pulseinterval of the pulses to be applied to any one of said inputs is alwaysgreater than a predetermined period, wherein said pulse sequence meansis so arranged that said sequence is repeated in a period no greaterthan said predetermined period, wherein there are at least three controloutputs of said pulse sequence means and wherein each said pulse outputmeans is constituted by a circuit unit including first gating meanshaving one output and at least three inputs, means connecting one saidinput to one of said control outputs of said pulse sequence means, firstand second bistable means each having an output, a set input, and are-set input, means connecting the outputs of said first and secondbistable means with respective further said inputs of said first gatingmeans, means connecting the output of said first gating means to therespective output of the device, said first gating means being arrangedto pass to said output a signal provided on the control output connectedto the first gating means only if enabling signals are applied by bothof said bistable means to said outputs thereof, means for detecting thecoincidence of a signal applied to the associated input of the devicewith a signal on a further one of said control outputs and for applyinga signal to the set input of said first bistable means on detecting suchcoincidence thereby to set the latter in its state providing an enablingsignal at its output, means for applying a signal to the re-set input ofsaid second bistable means to throw the latter into its state providingan inhibiting signal at its output, on the occurrence of a signal atsaid output of said first gating means and means for detecting thecoincidence of the occurrence of a signal on a yet further one of saidcontrol outputs with the absence of a signal on the associated input ofthe device, and for applying a signal to the re-set input of said firstbistable means and to the set input of said second bistable means ondetection of such a coincidence, said one control output, said furthercontrol output and said yet further control output being so selected foreach said circuit unit that in said sequence a signal will appear atsaid yet further one of said control outputs after the appearance of asignal at said further control output, each said circuit unit having itssaid first gating means connected to a different one of said controloutputs of said pulse sequence.

6. The apparatus of claim wherein each said circuit unit comprises afirst NAND gate, having an output and two inputs, means connecting onesaid input to said further control output (with respect to the circuitunit concerned) and means connecting its other said input to theassociated input of the device, means connecting the set input of saidfirst bistable means to the output of said first NAND gate, a secondNAND gate and means connecting the reset input of said first bistablemeans and the set input of said second bistable means to the output of asaid second NAND gate, said second NAND gate having two inputs, meansconnecting one of said inputs to said yet further control output (withrespect to the circuit unit concerned), an invertor and means connectingthe other of said second NAND gate via the invertor to the associatedinput of the device.

7. The apparatus of claim 1 wherein at least said first predeterminednumber is variable to vary the proportions of the blend.

8. The apparatus of claim 1 wherein each said dispehsing means includesa flow line, and flow controlling means selectively operable to preventflow of the respective substance therethrough, to restrict flowtherethrough to a predetermined extent and to allow unrestricted flowtherethrough, both of said dispensing means being arranged to dispenseat substantially equal rates in equivalent states of said flowcontrolling means, and switching means operable alternatively to connectsaid first counting means to either of said outputs of said device andto vary the control of said flow controlling means by said first andsecond counter means in such a way that when, in operation of theapparatus said second counting means has counted said secondpredetermined number of pulses, the flow control means of whicheverdispenser has its transducer arranged, by virtue of the state of saidswitching means, to supply its pulses via said device to said firstcounter means, is thereby placed in its state allowing unrestricted flowtherethrough and thereafter remains in its latter state until at least asubstantial proportion of said first predetermined number of pulses havebeen counted by said first counting means, while at the same time theother of said dispensing means is maintained in its state restrictingflow therethrough.

9. The apparatus of claim 8 wherein said control means is arranged atleast after cutting off the flow from the dispensing means associatedwith the transducer providing the pulses counted by said first counterto maintain the flow controlling means of the other dispenser in itsstate permitting full flow until said second predetermined number ofpulses has been counted by said second counting means and thereafter toreturn the latter flow controlling means to its state permitting onlyrestricted flow.

10. The apparatus of claim 1 wherein said control means includes meansarranged when a predetermined proportion of said first predeterminednumber of pulses has been counted by said first counting means to changethe flow controlling means of the dispensing means associated with thetransducer providing the pulses being counted by said first countingmeans to its state permitting only restricted flow and to change thelatter flow controlling means to its state preventing flow once saidfirst predetermined number of pulses has been counted by said firstcounting means.

11. The apparatus of claim 1 wherein said first counting means comprisesa counter and has associated therewith means for providing an outputsignal of a second value when the count in said counter reaches orexceeds said first predetermined number, and otherwise providing anoutput signal of a first value, and wherein said one dispensing meansincludes first flow control means having an input arranged to receivethe latter output signals, said first flow control means being arrangedin the presence of a signal of said second value to prevent flow of therespective substance from said dispenser means and in the presence of asignal of said first value to allow such flow, said second countingmeans being arranged each time said second predetermined number ofpulses has been counted thereby to pass a re-setting signal to saidfirst counting means to re-set the latter to zero.

12. The apparatus of claim 1 1 wherein said means associated with saidcounter in said first counting means includes register means in whichsaid first predetermined number can be set, and comparator meansarranged to provide said output signal of said second value when thenumber in said counter equals or exceeds the number in said register andotherwise to provide a signal of said first value.

13. The apparatus of claim 12 wherein said register means includes meansfor selecting the dispensing means which passes the substance providingthe minor portion of the desired blend as said one dispensing meanswhich includes first flow control means having an input to receive theoutput signal from said comparator.

14. The apparatus of claim 11 wherein each said dispensing means hasassociated therewith respective flow controlling means having a firstand a second input and means arranged in the presence of a signal of afirst value on both of said inputs to allow unrestricted flow throughsaid dispensing means, arranged in the presence of a signal of saidfirst value on said first input and a signal of a second value on saidsecond input to allow restricted flow through said dispensing means, andarranged in the presence of a signal of said second value on said firstinput to prevent flow through said dispensing means, said comparatormeans being arranged to provide said output signal of said second valueon a first output line associated therewith when the count in said firstcounter means equals or exceeds said first predetermined value thereof,said comparator means further being arranged to provide an output signalof said second value on a second output line associated therewith whenthe count in said first counter means reaches or exceeds a predeterminedproportion of said first predetermined number and otherwise to provideon said second output line a signal of said first value, switching meansoperable to selectively connect said second input of one of said flowcontrolling means to said second output line and at the same time toconnect said second input of the flow controlling means not so connectedto the output of invertor means connected to said second output line,further switching means operable to selectively connect one of theoutputs of said pulse capture unit to said counter means and yet furtherswitching means operable to selectively connect said first input of oneof said flow controlling means with said first output line of saidcomparator means, said switching means being ganged so that if the firstinput of the flow controlling means, of one of said dispensing means isconnected to said first output line, the first counter means isconnected to countthe pulses from the transducer of the latterdispensing means and said second input of the latter flow controllingmeans is connected to the output of said invertor means, whereas saidsecond input of the other flow controlling means is connected to saidsecond output line whereby as long as the count in said first counter isless than said predetermined proportion of said predetermined number,the dispensing means whose transducer is provid ing the pulses beingcounted by said first counting means has its flow controlling means setto allow full flow while the other dispensing means has its flowcontrolling means set to allow restricted flow, and whereby when saidpredetermined proportion has been reached the dispensing means whosetransducer is providing the pulses being counted by said first countermeans has its flow controlling means set to restrict flow, while theother flow controlling means is set to allow full flow, and when saidfirst predetermined number is reached the dispensing means whosetransducer is providing the pulses being counted by said first countermeans has its flow controlling means set to prevent flow.

15. The apparatus of claim 1 wherein each output of said pulse captureunit is also connected to a respective calculating device adapted tofunction as a divider the divisor of which is selected to correspond tothe price per unit quantity of the respective substance, the outputs ofsaid calculating devices being added via an OR gate in a counter wherebythe price of the total amount of the blended substances dispensed iscounted.

1. Apparatus for controlling the blending of two flowable substances,comprising separate dispensing means for each of said substances, acontrol means for at least one of said dispensing means operableselectively to cause said one dispensing means to dispense itsrespective substance and to arrest dispensing of its respectivesubstance, a transducer associated with each of said dispensing meansand arranged to produce a pulse each time a predetermined quantity ofthe respective substance is dispensed, a pulse capture unit having twoinputs each connected to a respective one of said transducers forreceiving pulses produced thereby and corresponding outputs at whichpulses are produced corresponding to the pulses applied to thecorresponding input, said pulses appearing at the respective outputs ofsaid pulse capture unit being noncoincident first counting means forcounting the pulses appearing on one of the corresponding outputs ofsaid pulse capture unit and corresponding to the pulses produced by thetransducer associated with said one dispensing means, second countingmeans for counting together the pulses appearing on both of saidcorresponding outputs of the pulse capture unit, said second countingmeans having associated therewith means arranged to operate the controlmeans for said one dispensing means each time that a secondpredetermined number of pulses has been counted by said second countingmeans since the preceding operation of said control means and said firstcounting means Having associated therewith means arranged to operatesaid control means for said one dispensing means to cause tha latter tocease dispensing when a first predetermined number of pulses smallerthan said second predetermined number has been counted thereby since thepreceding operation of said control means by said means associated withsaid second counting means, the relative mean flow rates of saiddispensing means during each period in which both dispensers aredispensing being such that the ratio of the mean flow through said onedispensing means to the mean total flow in said period is greater thanthe ratio of quantity of substance dispensed by said one dispensingmeans to the total quantity in the desired blend, and said first andsecond predetermined numbers being in the last mentioned ratio.
 2. Theapparatus of claim 1 wherein said pulse capture unit includes respectivepulse output means associated with each said input and a respective oneof said outputs, pulse sequence means for operating said pulse outputmeans repeatedly at different times, each said pulse output meansincluding means for detecting the occurrence of a pulse signal on itsassociated input and for storing said signal until operated by saidpulse sequence means, each said pulse output means including means fordelivering a signal to the associated output, if and only if a signalhas occurred at its associated input since the preceding operationthereof by said pulse sequence means said pulse sequence means beingarranged so that no two of said pulse output means are operable therebyat the same time, whereby the device will produce at each of saidoutputs thereof a train of pulses each corresponding to a respectivepulse at the associated input of the device and pulses on respectivesaid outputs are noncoincident
 3. The apparatus of claim 2 wherein saidpulse sequence means has a plurality of control outputs and is arrangedto produce pulse signals at said control outputs in a repeatingsequence, and each said pulse output means is arranged to be operated todeliver a pulse at the associated output of the device if a signal isstored in said means associated with said output, on the occurrence of apulse on an associated one of said further outputs of said pulsesequence means.
 4. The apparatus of claim 3 wherein said pulse sequencemeans comprises an oscillator, a counter for counting the periods ofsaid oscillator and a decoder driven by said counter decoder having aplurality of outputs constituting said control outputs of the pulsesequence means, the decoder being arranged to apply pulse signals in arepeating sequence to said control outputs thereof as successiveoscillator periods are counted by said counter.
 5. The apparatus ofclaim 3 for use where the pulse length and pulse interval of the pulsesto be applied to any one of said inputs is always greater than apredetermined period, wherein said pulse sequence means is so arrangedthat said sequence is repeated in a period no greater than saidpredetermined period, wherein there are at least three control outputsof said pulse sequence means and wherein each said pulse output means isconstituted by a circuit unit including first gating means having oneoutput and at least three inputs, means connecting one said input to oneof said control outputs of said pulse sequence means, first and secondbistable means each having an output, a set input, and a re-set input,means connecting the outputs of said first and second bistable meanswith respective further said inputs of said first gating means, meansconnecting the output of said first gating means to the respectiveoutput of the device, said first gating means being arranged to pass tosaid output a signal provided on the control output connected to thefirst gating means only if enabling signals are applied by both of saidbistable means to said outputs thereof, means for detecting thecoincidence of a signal applied to the associated input of the devicewith a signal on a Further one of said control outputs and for applyinga signal to the set input of said first bistable means on detecting suchcoincidence thereby to set the latter in its state providing an enablingsignal at its output, means for applying a signal to the re-set input ofsaid second bistable means to throw the latter into its state providingan inhibiting signal at its output, on the occurrence of a signal atsaid output of said first gating means and means for detecting thecoincidence of the occurrence of a signal on a yet further one of saidcontrol outputs with the absence of a signal on the associated input ofthe device, and for applying a signal to the re-set input of said firstbistable means and to the set input of said second bistable means ondetection of such a coincidence, said one control output, said furthercontrol output and said yet further control output being so selected foreach said circuit unit that in said sequence a signal will appear atsaid yet further one of said control outputs after the appearance of asignal at said further control output, each said circuit unit having itssaid first gating means connected to a different one of said controloutputs of said pulse sequence.
 6. The apparatus of claim 5 wherein eachsaid circuit unit comprises a first NAND gate, having an output and twoinputs, means connecting one said input to said further control output(with respect to the circuit unit concerned) and means connecting itsother said input to the associated input of the device, means connectingthe set input of said first bistable means to the output of said firstNAND gate, a second NAND gate and means connecting the reset input ofsaid first bistable means and the set input of said second bistablemeans to the output of a said second NAND gate, said second NAND gatehaving two inputs, means connecting one of said inputs to said yetfurther control output (with respect to the circuit unit concerned), aninvertor and means connecting the other of said second NAND gate via theinvertor to the associated input of the device.
 7. The apparatus ofclaim 1 wherein at least said first predetermined number is variable tovary the proportions of the blend.
 8. The apparatus of claim 1 whereineach said dispensing means includes a flow line, and flow controllingmeans selectively operable to prevent flow of the respective substancetherethrough, to restrict flow therethrough to a predetermined extentand to allow unrestricted flow therethrough, both of said dispensingmeans being arranged to dispense at substantially equal rates inequivalent states of said flow controlling means, and switching meansoperable alternatively to connect said first counting means to either ofsaid outputs of said device and to vary the control of said flowcontrolling means by said first and second counter means in such a waythat when, in operation of the apparatus said second counting means hascounted said second predetermined number of pulses, the flow controlmeans of whichever dispenser has its transducer arranged, by virtue ofthe state of said switching means, to supply its pulses via said deviceto said first counter means, is thereby placed in its state allowingunrestricted flow therethrough and thereafter remains in its latterstate until at least a substantial proportion of said firstpredetermined number of pulses have been counted by said first countingmeans, while at the same time the other of said dispensing means ismaintained in its state restricting flow therethrough.
 9. The apparatusof claim 8 wherein said control means is arranged at least after cuttingoff the flow from the dispensing means associated with the transducerproviding the pulses counted by said first counter to maintain the flowcontrolling means of the other dispenser in its state permitting fullflow until said second predetermined number of pulses has been countedby said second counting means and thereafter to return the latter flowcontrolling means to itS state permitting only restricted flow.
 10. Theapparatus of claim 1 wherein said control means includes means arrangedwhen a predetermined proportion of said first predetermined number ofpulses has been counted by said first counting means to change the flowcontrolling means of the dispensing means associated with the transducerproviding the pulses being counted by said first counting means to itsstate permitting only restricted flow and to change the latter flowcontrolling means to its state preventing flow once said firstpredetermined number of pulses has been counted by said first countingmeans.
 11. The apparatus of claim 1 wherein said first counting meanscomprises a counter and has associated therewith means for providing anoutput signal of a second value when the count in said counter reachesor exceeds said first predetermined number, and otherwise providing anoutput signal of a first value, and wherein said one dispensing meansincludes first flow control means having an input arranged to receivethe latter output signals, said first flow control means being arrangedin the presence of a signal of said second value to prevent flow of therespective substance from said dispenser means and in the presence of asignal of said first value to allow such flow, said second countingmeans being arranged each time said second predetermined number ofpulses has been counted thereby to pass a re-setting signal to saidfirst counting means to re-set the latter to zero.
 12. The apparatus ofclaim 11 wherein said means associated with said counter in said firstcounting means includes register means in which said first predeterminednumber can be set, and comparator means arranged to provide said outputsignal of said second value when the number in said counter equals orexceeds the number in said register and otherwise to provide a signal ofsaid first value.
 13. The apparatus of claim 12 wherein said registermeans includes means for selecting the dispensing means which passes thesubstance providing the minor portion of the desired blend as said onedispensing means which includes first flow control means having an inputto receive the output signal from said comparator.
 14. The apparatus ofclaim 11 wherein each said dispensing means has associated therewithrespective flow controlling means having a first and a second input andmeans arranged in the presence of a signal of a first value on both ofsaid inputs to allow unrestricted flow through said dispensing means,arranged in the presence of a signal of said first value on said firstinput and a signal of a second value on said second input to allowrestricted flow through said dispensing means, and arranged in thepresence of a signal of said second value on said first input to preventflow through said dispensing means, said comparator means being arrangedto provide said output signal of said second value on a first outputline associated therewith when the count in said first counter meansequals or exceeds said first predetermined value thereof, saidcomparator means further being arranged to provide an output signal ofsaid second value on a second output line associated therewith when thecount in said first counter means reaches or exceeds a predeterminedproportion of said first predetermined number and otherwise to provideon said second output line a signal of said first value, switching meansoperable to selectively connect said second input of one of said flowcontrolling means to said second output line and at the same time toconnect said second input of the flow controlling means not so connectedto the output of invertor means connected to said second output line,further switching means operable to selectively connect one of theoutputs of said pulse capture unit to said counter means and yet furtherswitching means operable to selectively connect said first input of oneof said flow controlling means with said first output line of saidcomparator means, said switching means beIng ganged so that if the firstinput of the flow controlling means, of one of said dispensing means isconnected to said first output line, the first counter means isconnected to count the pulses from the transducer of the latterdispensing means and said second input of the latter flow controllingmeans is connected to the output of said invertor means, whereas saidsecond input of the other flow controlling means is connected to saidsecond output line whereby as long as the count in said first counter isless than said predetermined proportion of said predetermined number,the dispensing means whose transducer is providing the pulses beingcounted by said first counting means has its flow controlling means setto allow full flow while the other dispensing means has its flowcontrolling means set to allow restricted flow, and whereby when saidpredetermined proportion has been reached the dispensing means whosetransducer is providing the pulses being counted by said first countermeans has its flow controlling means set to restrict flow, while theother flow controlling means is set to allow full flow, and when saidfirst predetermined number is reached the dispensing means whosetransducer is providing the pulses being counted by said first countermeans has its flow controlling means set to prevent flow.
 15. Theapparatus of claim 1 wherein each output of said pulse capture unit isalso connected to a respective calculating device adapted to function asa divider the divisor of which is selected to correspond to the priceper unit quantity of the respective substance, the outputs of saidcalculating devices being added via an OR gate in a counter whereby theprice of the total amount of the blended substances dispensed iscounted.